The use of rotating polygon scanning mirrors in laser printers to provide a beam sweep or scan of the image of a modulated light source across a photoresisted medium, such as a rotating drum, is well known. More recently, there have been efforts to use a much less expensive flat member with a single reflective surface, such as a MEMS resonant oscillating mirror to provide the scanning beam. Other devices using resonant oscillating members, other than mirrors, may also benefit from this invention. These torsional hinged resonant scanning devices provide excellent performance at a very advantageous cost. However, every new technology has its own set of problems and resonant torsional hinged devices, such as mirrors, are no exception.
As an example, inertially driven torsional hinged resonant devices made of silicon exhibit unusually high mechanical gain. Further, such resonant devices can readily be driven inertially through the support or anchor regions. However, as will be appreciated by those skilled in the art, the power required to drive the device to a required angular position is a function of the stiffness of the torsional hinges at the anchor regions that support the device and stiffness of the anchor region. Therefore, as customers demand larger mirrors or other oscillating devices with higher and higher resonant frequencies, the torsional hinges must be made stiffer. Typically, the greatest portion of the actuator or drive power is used to bend the anchor regions to provide the rotational motion at the hinge attachment regions of the anchor. Since a favored source of power for an inertial drive is a piezoelectric element, it will be appreciated that as greater drive power is required, greater drive voltages are also required to drive the piezoelectric element. For battery powered applications, such high voltage requirements are a problem.
Therefore, method and structures that facilitate the use of high frequency large resonant devices with a large angular movement without a corresponding increase in drive power would be advantageous.
As will also be appreciated, the resonant frequency of such an oscillating device cannot be precisely set by manufacturing methods. Consequently, a method of adjusting the resonant frequency would be a significant improvement and would improve yield.